One of the more useful 3D Touch tricks is the ability to preview a link before opening it, allowing iPhone users a way to quickly see a preview of a webpage link before loading the entire thing in Safari. This can be activated from an email, from messages, or Safari itself, and it helps to determine if a link is what you’re looking for or worth opening. It’s use case is quite similar to previewing links with multitouch on the Mac, and it works much the same as well.
Previewing links with 3D Touch requires an iPhone 6s or better, since the feature obviously requires a 3D Touch capable screen

Open Safari to any web page (capmac.net for example) on the iPhone

Gently press and hold on a link to activate the preview “peak”, you’ll see the link target webpage load in a little hovering preview screen quickly

Firm press to visit the link in question, otherwise let go to return to the webpage you were reading before

You can also swipe up in the peak preview to see more options including Open in New Tab, Add to Reading List, or Copy, which copies the URL being previewed.